Bernhard Biersack

4-(3-Halo/amino-4,5-dimethoxyphenyl)-5-aryloxazoles and -N-methylimidazoles that are cytotoxic against combretastatin A resistant tumor cells and vascular disrupting in a cisplatin resistant germ cell tumor model.

New combretastatin A analogues featuring oxazole or N-methylimidazole bridged Z-alkenes and halo- or amino-substituted A-rings were tested against various cancer cell lines and in testicular germ cell tumor xenografts in mice. Imidazoles with 3-halo-4,5-dimethoxy substituted A-rings and 3-amino-4-methoxy substituted B-rings (7b and 8b) were efficacious at nanomolar concentrations against cells of combretastatin A refractory HT-29 colon carcinoma, multidrug-resistant MCF-7/Topo breast carcinoma, and cisplatin-resistant 1411HP testicular germ cell tumor. They induced apoptosis and inhibited tubulin polymerization. While well tolerated by mice at high doses, these imidazoles initiated extensive intratumoral hemorrhage and regressions of highly vascularized 1411HP xenografts.

Gold(I)-NHC complexes of antitumoral diarylimidazoles: structures, cellular uptake routes and anticancer activities.

Five new heterocyclic gold carbene complexes were prepared, four chlorido-[1,3-dimethyl-4,5-diarylimidazol-2-ylidene]gold complexes 6a-d and a chlorido-[1,3-dibenzylimidazol-2-ylidene]gold complex 11, and three of them were characterised by X-ray single crystal analyses. They were tested for cytotoxicity against a panel of four human cancer cell lines and non-malignant fibroblasts, for tubulin interaction, and for the pathways of their uptake into 518A2 melanoma cells. All complexes showed cytotoxic activity in the micromolar IC(50) range with distinct selectivities for certain cell lines. In stark contrast to related metal-free 1-methyl-4,5-diarylimidazoles, the complexes 6 and 11 did not noticeably inhibit the polymerisation of tubulin to give microtubules. The cellular uptake of complexes 6 occurred mainly via the copper transporter (Ctr1) and the organic cation transporters (OCT-1/2). Complex 11 was accumulated preferentially via the organic cation transporters and by Na(+)/K(+)-dependent endocytosis. The new gold carbene complexes seem to operate by a mechanism different from that of the parent 1-methylimidazolium ligands.

Coinage metal complexes against breast cancer.

Breast cancer is still the leading cause of cancer deaths among women worldwide, and new therapies to treat this dangerous disease are desperately needed. The serendipitously found anticancer drug cisplatin and its second-generation congener carboplatin appear to be promising drug systems for the treatment of breast tumors, in particular of multidrug resistant and highly aggressive triple-negative subtypes. In the wake of these platinum drugs, complexes of the coinage metals copper, silver, and gold were developed that showed enhanced selectivity for breast cancer while causing fewer and weaker side-effects. This review takes stock of the latest developments in the field of coinage metal anticancer drugs with an emphasis on their biological and mechanistic aspects. Pertinent literature is covered up to 2012.

Anticancer Active Illudins: Recent Developments of a Potent Alkylating Compound Class

An overview of anticancer active spirocyclopropanes of the illudin class is provided. After a short introduction on the history and general chemistry of illudins M and S, new discoveries concerning their mode of action and metabolism are reported as well as new synthetic endeavors towards derivatives with improved selectivity for and efficacy against cancer cells. In addition, common and recently tapped biological sources and isolation procedures for known and new illudins are discussed. Pertinent literature is covered up to 2010.

Adjusting the DNA Interaction and Anticancer Activity of Pt(II) N-Heterocyclic Carbene Complexes by Steric Shielding of the Trans Leaving Group.

Five platinum(II) complexes bearing a (1,3-dibenzyl)imidazol-2-ylidene ligand but different leaving groups trans to it were examined for cytotoxicity, DNA and cell cycle interference, vascular disrupting properties, and nephrotoxicity. The cytotoxicity of complexes 3a-c increased with the steric shielding of their leaving chloride ligand, and complex 3c, featuring two triphenylphosphanes, was the most efficacious, with submicromolar IC50 concentrations. Complexes 3a-c interacted with DNA in electrophoretic mobility shift and ethidium bromide binding assays. The cationic complex 3c did not bind coordinatively to DNA but led to its aggregation, damage that is not amenable to the usual repair mechanisms. Accordingly, it arrested the cell cycle of melanoma cells in G1 phase, whereas cis-dichlorido[(1,3-dibenzyl)imidazol-2-ylidene](dimethyl sulfoxide) platinum(II) 3a induced G2/M phase arrest. Complex 3c also disrupted the blood vessels in the chorioallantoic membrane of fertilized chicken eggs. Ex vivo studies using precision-cut tissue slices suggested the nephrotoxicities of 3a-c to be clinically manageable.

Metal complexes of natural melophlins and their cytotoxic and antibiotic activities

Complexes of the natural melophlins A and C with Mg, Zn, Ga, La and Ru were prepared, characterized and tested for antimicrobial and cytotoxic effects. The lanthanum complex La(melophlinato C)(3) and the ruthenium complex chlorido(eta(6)-p-cymene)(melophlinato C)ruthenium(II) inhibited cells of human A-498 kidney cancer at IC(50)=0.54 microM and 1.0 microM, respectively, and so distinctly better than free melophlin C. Another synergistic effect of coordinating melophlins to bioactive metals was found in the growth inhibition of the melophlin C-resistant bacterium Micrococcus luteus by Ga, La and Ru complexes of melophlin C.

Pt(II) complexes of a combretastatin A-4 analogous chalcone: effects of conjugation on cytotoxicity, tumor specificity, and long-term tumor growth suppression.

Three dichlorido(6-aminomethylnicotinate)platinum complexes 6 comprising a combretastatin A-4 analogous chalcone were tested on a panel of 21 tumor cell lines from 9 entities. Parent chalcone 1a and the directly linked conjugate 6a exhibited excellent antiproliferative activities, similar in magnitude [average log(IC(50)) values of -7.3 (1a) and -7.0 (6a)] and cell line specificity but slightly different in the mechanism of apoptosis induction. While 1a and 6a caused an equally fast rise in caspase-9 in the tested cancer cell lines, the downstream effector caspase-3 built up faster in cells treated with 1a compared to 6a, yet reached an equal end level. They also had different long-term effects on the regrowth of cancer cells treated with a single dose. In contrast, conjugates 6b,c featuring longer spacers between the Pt complex and the chalcone moieties were less antiproliferative than 6a.

Anticancer action of garcinol in vitro and in vivo is in part mediated through inhibition of STAT-3 signaling

Garcinol, obtained from Garcinia indica, has exhibited some promising anticancer activity. In particular, our earlier work has demonstrated its ability to inhibit cell proliferation and induction of apoptosis in multiple cancer cell lines representative of breast, prostate, as well as pancreatic cancers. However, its exact mechanism of action remains largely unclear. Here we show that garcinol also targets signal transducer and activator of transcription-3 (STAT-3) signaling pathway. STAT-3 is frequently found to be activated in many cancer types and this is the first report on such action of garcinol leading to its anticancer effects. Garcinol inhibited total, as well as phosphorylated, STAT-3 in breast, prostate and pancreatic cancer cell lines and was also found to inhibit cell invasion of all the cancer cell lines tested. STAT-3 phosphorylation was inhibited by garcinol in a dose-dependent manner. We also observed an inhibitory effect of garcinol on IL-6-induced STAT-3 phosphorylation and production of urokinase-type plasminogen activator, vascular endothelial growth factor and matrix metalloproteinase-9, which might explain the reduced invasion and aggressiveness of cells treated with garcinol. The results were further verified in vivo using MDA-MB-231 breast cancer mouse xenograft model where administration of garcinol significantly inhibited tumor growth, and western blot analysis of remnant tumor lysates showed reduced STAT-3 expression and activation. These results suggest that garcinol may have translational potential as chemopreventive or therapeutic agent against multiple cancers and inhibition of STAT-3 signaling pathway is one of the mechanisms by which garcinol exerts its anticancer effects.

Arene)Ru(II) complexes of epidermal growth factor receptor inhibiting tyrphostins with enhanced selectivity and cytotoxicity in cancer cells.

Ru(eta6-arene) complexes of epidermal growth factor receptor (EGFR) inhibiting tyrphostins 1a and 1b were prepared, characterized and tested for DNA interaction and bioactivity in four human tumor cell lines. The intrinsic cytotoxicity and cell line selectivity of o-hydroxyanisol 1a was greatly enhanced in its Ru(eta6-p-cymene) complex 2a and in its Ru(eta6-toluene) complex 3a. Complex 2a was particularly efficacious against multi-drug resistant EGFR(+) MCF-7/Topo breast carcinoma cells and also against mTOR-dependent EGFR(-) HL-60 leukemia cells. Complex 3a showed enhanced activity only against 518A2 melanoma cells and HL-60 cells, which are both known to express the mTOR protein. DNA was strongly metallated (ca. 1.7-2%) by all new Ru complexes without undergoing topological changes. Apparently, by complexation to Ru fragments tyrphostin derivatives can address additional biological targets in a manner instrumental to antitumoral strategies.

Gold(I) Biscarbene Complexes Derived from Vascular‐Disrupting Combretastatin A‐4 Address Different Targets and Show Antimetastatic Potential

Gold N‐heterocyclic carbene (NHC) complexes are an emerging class of anticancer drugs. We present a series of gold(I) biscarbene complexes with NHC ligands derived from the plant metabolite combretastatin A‐4 (CA‐4) that retain its vascular‐disrupting effect, yet address different cellular and protein targets. Unlike CA‐4, these complexes did not interfere with tubulin, but with the actin cytoskeleton of endothelial and cancer cells. For the highly metastatic 518A2 melanoma cell line this effect was accompanied by a marked accumulation of cells in the G1 phase of the cell cycle and a suppression of active prometastatic matrix metalloproteinase‐2. Despite these mechanistic differences the complexes were as strongly antivascular as CA‐4 both in vitro in tube formation assays with human umbilical vein endothelial cells, and in vivo as to blood vessel disruption in the chorioallantoic membrane of chicken eggs. The antiproliferative effect of the new gold biscarbene complexes in a panel of six human cancer cell lines was impressive, with low sub‐micromolar IC50 values (72 h) even against CA‐4‐refractory HT‐29 colon and multidrug‐resistant MCF‐7 breast carcinoma cells. In preliminary studies with a mouse melanoma xenograft model the complexes led to significant decreases in tumor volume while being very well tolerated.